In order to improve impact mitigation effects, anti-sliding effects or texture of molded products, thermoplastic rubber compositions are laminated on thermoplastic resin molded products.
Conventionally, styrene-based thermoplastic rubbers or olefin-based rubbers having superior flexibility were laminated on thermoplastic resin molded products.
Additionally, a thermoplastic rubber composition may be laminated on or bonded to a thermoplastic resin to manufacture molded products. Examples of such a method include a coextrusion molding method, a two-color molding method, an insert injection molding method, a double injection molding method, etc. The coextrusion molding method is a molding method wherein two materials, i.e., a thermoplastic resin and a thermoplastic rubber composition are separately extruded in two extruders and are joined in a die so that the two materials are molded through heat-welding. The two-color molding method is a molding method wherein two-layer molded products are molded by heat-welding two materials in a mold using an injection molding machine equipped with two injection buckets. The insert injection molding method is a molding method wherein two-layer molded products are manufactured by injecting a thermoplastic rubber composition into a mold into which a thermoplastic resin molded product molded using an injection machine is inserted and heat-welding the same. The double injection molding method is a molding method wherein molded products are manufactured by sequentially injection-molding two resin types in a mold.
However, when such methods are used, a bonding property to a polyolefin-based resin is good as a styrene-based thermoplastic rubber does not have a polar functional group, but a bonding property to polycarbonate resin is very poor. Accordingly, when a complex is formed using the styrene-based thermoplastic rubber and a thermoplastic resin including a polar functional group such as the polycarbonate resin, unevenness may be formed in the complex or properties of a thermoplastic rubber may be deteriorated.
Conventionally, a styrene-based thermoplastic rubber composition was laminated on a polycarbonate resin using an adhesive. However, in this case, preparation process steps are added and preparation costs increase.
Accordingly, development of products is being tried using an alloy of a thermoplastic rubber and a resin, but, in this case, thermal characteristics are not satisfied at high temperature and softness of a product surface is deteriorated.
In order to address such problems, a technology of enhancing bonding between a polycarbonate resin or a polyacrylate resin and a styrene-based thermoplastic rubber without application of an adhesive using poly(styrene-b-ethylene-co-butylene-b-styrene)-g-(maleic anhydride) (SEBS-g-MA) as a compatibilizer, in which a styrene-ethylenebutylene-styrene block copolymer and a maleic anhydride, are graft-copolymerized, was developed. However, in this case, it is not easy to control hardness and a functional group of a maleic anhydride of SEBS-g-MA may cause side reaction depending upon processing conditions.
In addition, the hardness of the thermoplastic rubber composition should be controlled depending upon required characteristics of a final product. However, in conventional thermoplastic rubber compositions, it is not easy to control hardness thereof.
Accordingly, the present inventors developed a thermoplastic rubber composition wherein, when a thermoplastic resin and a thermoplastic rubber composition are bonded, a resin ingredient and a rubber ingredient may be directly bonded through strong adhesive force thereof without application of an adhesive, and, furthermore, hardness thereof may be easily controlled.